ous ways; for example, as below, where they are divided into two main divisions: A division, in which the parasite is known; and B division, in which the parasite is unknown.

A. PARASITE KNOWN.

I. Diseases caused by parasites belonging to the genus Piroplasma: (1) East coast fever (Koch), P. parvum; (2) Redwater or Texas fever, P. bigeminum (Theiler); (3) Biliary fever of horses, mules and donkeys, P. equi; (4) Malignant jaundice of dogs, P. canis.

II. Diseases caused by parasites belonging to the genus Trypanosome: (1) Nagana or tsetse-fly disease, T. brucei (Bradford and Plimmer); (2) Trypanosomiasis of cattle, T. theileri (Bruce).

B. PARASITE UNKNOWN.

I. Rinderpest.

II. Horse-sickness. Catarrhal fever of sheep; heart-water of sheep, goats and cattle.

I. DISEASES CAUSED BY PARASITES BELONGING TO THE GENUS PIROPLASMA.

1. East Coast Fever.

The first important stock disease I would draw your attention to, then, is east coast fever.

This name was given to it by Professor Robert Koch, of Berlin. In the Transvaal the disease is usually called Rhodesian redwater. This term is not a good one, since the disease is not restricted to Rhodesia, nor did it arise there, nor is this a disease similar to the ordinary redwater. Ten years ago, when I first came to South Africa, east coast fever was unknown in the Transvaal. The first known outbreak occurred only some three and a half years ago, when it broke out at Koomati and Neilspruit, in the Barberton district, and in the east of the colony. The disease had broken out some time previously in Rhodesia, and the outbreaks in both colonies were due to infection from Portuguese territory. Although this disease has only been introduced to the country during the last few years, it has already produced an enormous amount of damage

among stock, and is probably the most dangerous disease that the people of the Transvaal have to cope with at the present time, and for some years to come.

In the Annual Report of the Transvaal Department of Agriculture there is a most excellent report by Mr. Stockman, the then principal veterinary surgeon, on the work of the veterinary division for the year 1903-1904. A large part of this report is given up to east coast fever, and I must here express my indebtedness to Mr. Stockman for much of the following account of this disease. In the same annual report there is also an account by Dr. Theiler, the veterinary bacteriologist, of the experimental work. Messrs. Stockman and Theiler evidently worked together, and I must congratulate them on the immense amount of good, useful work done by them, and I would also congratulate the government on having had the services of two such accomplished and energetic gentlemen during the late troublesome times. Unfortunately for the Transvaal, Mr. Stockman has accepted the post of veterinary adviser to the board of agriculture in England, but I have no doubt his successor, Mr. Gray, from Rhodesia, will continue the good work begun by him.

East coast fever was first studied by Professor Koch at Dar-el-Salaam, in German East Africa, and he at first mistook it for ordinary redwater. It seems to occur as an endemic disease along a great part of the east coast of Africa, but appears to be restricted to a narrow belt along this coastline. The cattle inhabiting this region have become immune to the disease, and are, therefore, not affected by it. Cattle passing through the coast district to the interior, or brought to the coast district from the interior, are apt to take the disease and die. It was by the importation of cattle, therefore, which had passed through the

dangerous coast district that the disease was introduced into Rhodesia and into the Transvaal. On this map which I throw on the screen I have marked out the probable endemic area of this disease, and in the next slide the present distribution of the disease in the Transvaal is also marked out. Nature of the Disease.-This disease only attacks cattle, but in them is an exceedingly fatal malady; in every hundred cattle attacked only about five recover from the disease. The duration of the disease after the first symptoms have occurred is about ten days.

The cause of the disease is a minute blood parasite called the Piroplasma parvum (Theiler). This parasite lives in the interior of the red blood corpuscles.

I now throw on the screen a representation of the blood from a case of Rhodesian redwater, magnified about a thousand times, showing these small piroplasmata in the interior of the red blood corpuscles. As in the case of so many of these blood diseases, the parasite causing it is carried. from the sick to the healthy by means of a blood-sucking parasite. In this particular disease the tick which most commonly transfers the poison or living parasite from one animal to another is known as the 'brown tick,' Rhipicephalus appendiculatus. Koch supposed that the common 'blue tick' was the agent. The credit belongs to Dr. Lounsbury and Dr. Theiler of having shown that it is chiefly the 'brown tick' which acts as carrier; but Theiler has proved that R. simus is also able to transmit the disease. Without the intervention of a tick, as far as we know at present, it is quite impossible that the parasite of this disease can be transferred from one animal to another. For example, if we take a quantity of blood containing enormous numbers of these piroplasmata, and inject it into the blood circulation of a healthy

animal, the latter does not take the disease. In the same way, if cattle affected by east coast fever are placed among healthy cattle in a part of the country where none of these 'brown ticks' are found, the disease does not spread. It is evident, therefore, that some metamorphosis of the parasite must take place in the interior of the tick, and this new form of the parasite is introduced by the tick into a healthy animal, and so produces the disease. In this particular disease the virus or infective agent is not transmitted through the egg of the tick, as is the case in some of these parasitic diseases, but only in the intermediate stages of the tick's development; that is to say, the larva which emerges from the egg of the tick is incapable of giving the disease. What happens is this: the larva creeps on to an infected animal and sucks some of its blood. It then drops off, lies among the roots of the grass, and passes through its first moult. The nympha, which is the name given to the creature after its first moult, is capable of transferring the disease to a healthy animal; that is to say, if it crawls on to a healthy animal and sucks blood from it, it at the same time infects this healthy animal with the germ of east coast fever. In the same way, if a nympha sucks infected blood from a sick animal, it is able, after it has moulted into the adult stage or imago, again to give rise to the disease if placed, or if it crawls, upon a healthy animal.

The Life-history of the Brown Tick.-I throw on the screen a slide representing the four stages of the life-history of the brown tick: The egg, the larva, the nympha and the adult or imago. The eggs are laid on the surface of the ground by the adult females, who deposit several thousand at a time; and these hatch out naturally, if the weather is warm and damp, in twenty-eight days. But this period of incubation of the

eggs may vary very greatly owing to differences in temperature. Immediately after the larva is born it crawls to the summit of a blade of grass or grass stem, and there awaits the passage of some animal. If an ox passes by and grazes on the grass, the tick at once crawls on to the animal, and, having secured a favorable position, starts to suck the ox's blood. It remains on the ox for some three or more days, when, having filled itself with blood, it drops off and lies among the grass. The first moult,

As a

under favorable conditions, takes twentyone days, when the nympha emerges. In the same way the nympha crawls on to an animal and fills itself with blood. nympha it also remains on the animal for about three or four days. It again drops off into the grass, and at the end of eighteen days emerges from its second moult as the perfect adult male or female. The males and females again crawl on to an ox, where they mate. After this the female tick ingests a large quantity of blood, which is meant for the nourishment of the eggs, and again drops off, sometimes as early as the fourth day, into the surrounding grass. After about six days she lays her eggs in the ground, and the cycle begins again.

These ticks are very hardy, and in the intermediate stages can resist starvation for long periods, so that a larva or nympha or adult tick may remain perched at the end of a blade of grass for some months without finding an opportunity of transferring itself to a suitable animal. On this account it comes about that even if all infected cattle are removed from a field the ticks in that field will remain capable of transferring the infection to any healthy. cattle which may be allowed into this field for a period of about a year. At the end of a year or fifteen months, however, the infective ticks are all dead, and clean cattle may be allowed into the field without any

risk. If one takes these facts into consideration it will be seen that a single ox may spread this disease for a distance of some 200 miles, if trekking through the country at the average rate of ten miles a day. For example, an ox is infected by a tick; for fourteen days the animal remains apparently perfectly well; it has no signs of disease, nor has it any fever. It is capable of doing its ten miles' trek a day. At the end of fourteen days the temperature begins to rise, and the animal begins to sicken with the disease, but for the next six days the ox is, as a rule, able to do its ordinary day's march. During most of this time the brown ticks have been crawling on to this ox, becoming infected, and dropping off every three or four days. It can readily, therefore, be seen how much mischief a single infected animal can do to a country between the time of its being infected by the tick and its death some twenty-four days later. As a matter of experience, however, the disease has never been found to make a jump in this way of more than fifty or sixty miles, as, of course, it is very rare that a transport carrier will take his oxen more than that distance during the twenty days.

At the present time it may be said that there are about 500 infected farms in the Transvaal. During last year some 15,000 cattle died of the disease, and in the affected districts it may be said that there are still some 30,000 cattle alive. When one considers the value of the cattle dead of this disease, which may be said to be about £200,000, it is evident that money spent on the scientific investigation of the causes and prevention of stock diseases is money well spent. I am informed that all the South African governments are cutting down their estimates this year, and are inclined to reduce their veterinary staffs and the amounts devoted to research regarding

animal diseases. Ladies and gentlemen, if. this is so, I have no hesitation in saying that this is the maddest sort of economy and the shortest-sighted of policies.

Methods of Combating the Disease.During the last three years an immense amount of work has been done in the elucidation of this disease-how the animals are infected, how the poison is spread from the sick to the healthy, and so on. In 1903 Professor Koch was asked by the South African colonies to study this disease, in order to try to find some method of artificial inoculation or some other means of prevention. He did his work in Rhodesia, and especially directed his energies towards discovering some method of preventive inoculation. At first it was thought that he would be successful in this quest, as in his second report he announced that he had succeeded in producing a modified form of the disease by direct inoculation with the blood of sick and recovered animals. As you are all aware, the only method of conferring a useful immunity upon an animal is to make it pass through an attack of the disease itself, so modified as not to give rise to above a few deaths in every hundred inoculated. This is the method that has been employed in such diseases as rinderpest, anthrax, pleuro-pneumonia and many other diseases. The great difficulty in this disease in finding a method of preventive inoculation is the fact that the blood of an affected animal does not give rise to the disease in a healthy one when directly transferred under the skin of the latter. It is only after its passage through the body of the tick that the parasite is able to give rise to the disease in a healthy animal. It is evidently, on the face of it, difficult to so modify the parasite during its sojourn in the tick's body as to reduce its virulence to a sufficient degree.

Professor Koch in his third and fourth

reports recommended that cattle should be immunized by weekly or fortnightly inoculations of blood from recovered animals, extending over a period of five months. Even though this method of Koch had given the desired result, viz., that it rendered the inoculated cattle immune to the disease, it is evident that the method itself can hardly be made a practicable one on a large scale in the field. The expense and trouble of inoculating cattle on twenty different occasions would be very great. It is apparent now that Professor Koch fell into error through mixing up east coast fever with ordinary redwater. His plan of preventive inoculation was, however, tried on a large scale in Rhodesia by Mr. Gray, now the principal veterinary surgeon, Transvaal, and found to be useless. At present, therefore, we must look to some other means of preventing the disease and driving it out of the country than preventive inoculation.

Dipping.-Much can be done to prevent the spread of this disease by ordinary methods. For example, in the case of Texas fever in Queensland dipping cattle in solutions of arsenic or paraffin, in order to destroy the ticks, has met with very fair success; but in the case of this disease we can not expect to get as good results as in the case of redwater. The species of tick which conveys Texas fever remains on the same animal through all its moults, instead of falling to the ground between each different one. If it is not possible to spray or dip cattle oftener than once in ten or fifteen days, it is evident that ticks may crawl upon such animals, become infected, and drop off every three or four days, and so escape destruction by the dipping solution. At the same time every infected tick that is killed by spraying or dipping operations is a source of infection destroyed.

Fencing of Farms.-Again, the fencing